1. Field of the Invention
This invention relates to novel compositions comprising substantially pure hydrogen and substantially pure helium and their use as heat transfer fluids in a variety of applications.
2. Related Art
Pure or substantially pure helium has excellent heat transfer properties. For example, helium is typically employed to enhance fiber cooling during the optical fiber drawing process because it is chemically inert and because of its heat transfer properties. Of the common pure gases, only pure hydrogen has a higher thermal conductivity than pure helium. However, hydrogen is not as inert as helium and it is more hazardous to employ in certain gas-related heat transfer applications than any inert gas. Therefore, hydrogen is typically avoided as a gaseous heat transfer medium in some (but not all) cooling or heating process applications.
It is generally accepted that binary mixtures of helium (or hydrogen) with other gases will have better heat transfer coefficients than the pure gases themselves. See, for example, M. R. Vanco, xe2x80x9cAnalytical Comparison of Relative Heat-Transfer Coefficients and Pressure Drops of Inert Gases and Their Binary Mixtures, NASA TN D2677 (1965); F. W. Giacobbe, xe2x80x9cHeat Transfer Capability of Selected Binary Gaseous Mixtures Relative to Helium and Hydrogenxe2x80x9d, Applied Thermal Engineering Vol. 18, Nos. 3-4, pp.199-206 (1998); R. Holoboffet al., xe2x80x9cGas Quenching With Heliumxe2x80x9d, Advanced Materials and Processes, Vol.143, No. 2, pp.23-26 (1993). In particular, Holoboff et al. noted that in the context of a heat treating furnace, by changing to an optimum helium/argon mixture, a customer was able to heat treat parts that could not be processed as rapidly as when using argon alone, while maintaining lower operating costs than normally required when using 100% helium. In a separate example, the same authors also recognized the benefits of increasing the fan speed (gas circulation velocity) on specimen cooling rates when using pure helium and pure nitrogen in cooing applications. However, there is no teaching or suggestion of the influence of heat transfer fluid mixture velocity on cooling rate for optimized mixtures of heat transfer fluids.
For illustrative purposes, according to earlier theories the relative heat transfer capability of helium plus one other noble gas compared to pure helium may be seen in FIG. 1. In FIG. 1, pure helium has been arbitrarily assigned a relative heat transfer capability of 1.0 in order to deliberately avoid the use of a more complicated system of SI heat transfer units. So, if a binary gas mixture containing helium has a heat transfer capability of 2.0 (relative to pure helium), it is assumed from this data that gas mixture will be 2.0 times more effective in any heat transfer process employing that gaseous mixture instead of pure helium alone. And, as a simplified illustration of the potential helium savings using this data, if the best binary gas mixture contained only 50 percent (by volume or mole fraction) helium plus 50 percent of some other gas, only xc2xd of that gas mixture would be needed to perform the same cooling function as the pure helium alone. Therefore, only 25 percent of the helium that would have been required for a particular heat exchange process using pure helium would be needed during the same cooling process employing the gas mixture.
In FIG. 2, and also according to earlier theories, the optimum composition and approximate relative heat transfer capability of hydrogen plus one noble gas with respect to pure helium is illustrated. In FIG. 2, pure helium has also been arbitrarily assigned a relative heat transfer capability of 1.0. So, if a binary gas mixture containing only hydrogen and argon (but no helium) has a heat transfer capability of 1.4 (relative to pure helium), that gas mixture presumably will be 1.4 times more effective in any heat transfer process employing that gaseous mixture instead of pure helium alone. And, since no helium is required to produce this effect, the helium usage is cut to zero. Furthermore, since hydrogen and argon are typically much less expensive than helium, the overall cost of the hydrogen/argon coolant gas stream will tend to be negligible compared to a pure (or relatively pure) helium coolant gas steam.
It should be emphasized that the data presented in FIGS. 1 and 2 are theoretical and based on turbulent flow for all gases and gas mixtures considered. However, in the seminal work of R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena, pp. 392-393 (1960) it was pointed out that xe2x80x9cthe heat-transfer coefficient depends in a complicated way on many variables, including the fluid properties (k, xcexc, xcfx81, Cp), the system geometry, the flow velocity, the value of the characteristic temperature difference, and the surface temperature distribution.xe2x80x9d In engineering design, therefore, use of constant property idealization frequently leads to either a greater built in safety factor, or a dangerous situation if the other extreme is taken. See D. M. McEligot, et al., xe2x80x9cInternal Forced Convection to Mixtures of Inert Gasesxe2x80x9d, Int. J. Heat Mass Transfer, Vol. 20, pp. 475-486 (1977).
In light of the unexpected nature of heat transfer coefficients of fluids, it would be advantageous in many heat transfer situations common in engineering to employ a heat transfer fluid mixture consisting essentially of pure hydrogen and helium that can easily be changed in composition to take advantage of the heat transfer properties of hydrogen, without the dangerous explosive characteristics of pure hydrogen, or to reduce the cost of using pure helium.
In accordance with the present invention, compositions consisting essentially of substantially pure hydrogen and substantially pure helium are presented (that can be advantageously employed in heat transfer applications, such as glass fiber cooling applications) which significantly reduce the danger of using pure hydrogen while providing nearly the same heat transfer properties as pure hydrogen. As used herein the term xe2x80x9chydrogenxe2x80x9d means molecular hydrogen, or H2. It has been discovered, quite unexpectedly, that heat transfer fluid mixtures consisting essentially of hydrogen and helium, plus such optional fluids such as argon, when flowing past a heat transfer surface at very low bulk velocity or very high bulk velocity, exhibit heat transfer coefficients that are less than but close to that of the pure hydrogen flowing at the same bulk velocity. Therefore, while compositions of the invention might require slightly more heat transfer area than pure hydrogen to achieve the same characteristic temperature difference in a fluid being heated or cooled, since the inventive compositions are much less explosive than pure hydrogen, there is an opportunity for better overall safety and longevity of equipment. Alternatively, if the designer allows for a slightly higher characteristic temperature difference, no change in heat transfer area is required. Furthermore, due to significant improvements in the heat transfer coefficients of these gas mixtures over substantially pure hydrogen when flowing at bulk velocities between very low and very high bulk velocity, the heat transfer designer may decide to use the inventive compositions and vary a parameter, such as concentration, bulk velocity, system pressure, characteristic temperature difference, and the like, to suit high demand time periods. For example, during times of high cool air demand in the summer months, a refrigeration unit employing one of the compositions may vary the concentration ratio of gases and the bulk velocity to achieve a higher characteristic temperature difference (better cooling).
As used herein the term xe2x80x9ccoolingxe2x80x9d includes freezing. The term xe2x80x9cheatingxe2x80x9d includes boiling, vaporizing, and the like.
The term xe2x80x9csubstantially pure hydrogenxe2x80x9d means a composition that includes only impurities or additives in such amounts that do not substantially lesson the heat transfer characteristics of pure hydrogen. The term xe2x80x9csubstantially pure heliumxe2x80x9d means a composition that includes only impurities or additives in such amounts that do not substantially lesson the heat transfer characteristics of pure helium. An example of an impurity in hydrogen might be carbon monoxide, as when the substantially pure hydrogen is derived from a synthesis gas. An example of an impurity in helium might be methane, when the substantially pure helium is derived from natural gas.
A first aspect of the invention is a heat transfer fluid mixture consisting essentially of substantially pure hydrogen and substantially pure helium, wherein a concentration of hydrogen in the mixture is an amount wherein:
a) the mixture will not be capable of mixing with air in any proportions to produce a self-sustaining flammable or combustible mixture, or
b) wherein the concentration of hydrogen is sufficient to reduce the cost of the mixture to an amount substantially less than the cost of pure helium.
As used herein the term xe2x80x9ccombustiblexe2x80x9d means a mixture of the invention that will burn at any temperature, irrespective of its ease of ignition, while xe2x80x9cflammablexe2x80x9d means a mixture of the invention which is a member of a special group of combustible mixtures that ignite easily and burn rapidly. See Hawley""s Condensed Chemical Dictionary, Twelfth Edition (1993), page 525.
As used herein the term xe2x80x9csubstantially less than the cost of pure heliumxe2x80x9d means that the cost of the compositions of the invention are preferably 10 percent less than the cost of pure helium, more preferably 20 percent less, and even more preferably 50 percent less than the cost of pure helium.
The inventive heat transfer fluid mixtures preferably have hydrogen concentration ranging from about 0.1 mole percent to about 1 mole percent; mixtures having from about 1 mole percent to about 10 mole percent hydrogen; mixtures having from about 10 mole percent to about 20 mole percent hydrogen. Particularly preferred heat transfer fluid mixtures are those having hydrogen concentration ranging from about 20 mole percent to about 30 mole percent; those having hydrogen concentration ranging from about 30 mole percent to about 40 mole percent; those wherein the hydrogen has a concentration ranging from about 40 mole percent to about 50 mole percent; and those wherein the hydrogen has a concentration ranging from about 50 mole percent to about 99 mole percent.
In certain applications, such as optical fiber consolidation, the inventive heat transfer fluid mixtures preferably have no more than about 100 ppm water, more preferably no more than about 10 ppm water, and more preferably no more than about 1 ppm water.
A second aspect of the invention is a method of cooling or heating an item or material, the method comprising contacting the item or material with one of the heat transfer fluid mixtures of the invention, the contacting selected from the group consisting of directly contacting, indirectly contacting, and combinations thereof.
A third aspect of the invention is a method of cooling or heating an item traversing through a substantially confined space, the method comprising contacting the item with one of the heat transfer fluid mixtures of the invention, the contacting selected from the group consisting of directly contacting, indirectly contacting, and combinations thereof.
A fourth aspect of the invention is a method of cooling a cylindrical optical fiber traversing through a heat exchanger, the method comprising contacting the cylindrical optical fiber with a gas mixture of the invention, the contacting selected from the group consisting of directly contacting, indirectly contacting, and combinations thereof.
A fifth aspect of the invention is a method of improving the cooling of a substantially cylindrical optical fiber traversing through a heat exchange device, the method comprising the step of contacting the optical fiber with a gas mixture consisting essentially of substantially pure hydrogen and substantially pure helium, the contacting selected from the group consisting of directly contacting, indirectly contacting, and combinations thereof, and making an adjustment either intermittently or continuously of a parameter during the cooling, the parameter selected from the group consisting of composition of the gas mixture, flow rate of the gas mixture into the heat exchange device, an amount of gas mixture contacting the fiber in counter-current fashion, an amount of gas mixture contacting the fiber in co-current fashion, composition of the gas mixture contacting the fiber in counter-current fashion, composition of the gas mixture contacting the fiber in co-current fashion, a temperature of the gas mixture being injected into the heat exchange device, a temperature of the gas mixture before contacting the fiber in counter-current fashion, a temperature of the gas mixture during contacting the fiber in counter-current fashion, a temperature of the gas mixture after contacting the fiber in counter-current fashion, a temperature of the gas mixture before contacting the fiber in a co-current fashion, a temperature of the gas mixture during contacting the fiber in a co-current fashion, a temperature of the gas mixture after contacting the fiber in a co-current fashion, a pressure of the gas mixture injected into the heat exchange device, a pressure of the gas mixture contacting the fiber in countercurrent fashion, and a pressure of the gas mixture contacting the fiber in a co-current fashion.
A sixth aspect of the invention is a method of improving cooling or heating of any hot or cold object or material in contact with a stagnant or flowing gas mixture in a confined space, the method comprising directly or indirectly contacting the object with a gas mixture consisting essentially of substantially pure hydrogen and substantially pure helium, and making an adjustment either intermittently or continuously of a parameter during the cooling or heating process, the parameter selected from the group consisting of a composition of the gas mixture, a flow rate of the gas mixture in contact with the object, an amount of gas mixture contacting the object, a composition of the gas mixture contacting the object, a temperature of the gas mixture injected into the confined space, a temperature of the gas mixture before contacting the object, a temperature of the gas mixture during contacting the object, a temperature of the gas mixture after contacting the object, a pressure of the gas mixture entering the confined space, and a pressure of the gas mixture contacting the object. One particularly preferred embodiment is that wherein the parameter adjustment is made automatically or manually based upon a measured parameter of the object or material that changes during the cooling or heating process.
Other aspects and advantages of the invention will become apparent after review of the description, drawing figures, and claims herein.